26.17.02.08

.08 Stormwater Management Measures.

A. The ESD planning techniques and practices and structural stormwater management measures established in this regulation and the Design Manual shall be contained in all county and municipal ordinances. Each ordinance shall require that a developer demonstrate that ESD has been implemented to the MEP and, only where absolutely necessary, is a structural BMP used in developing a stormwater management plan.

B. ESD Planning Techniques and Practices.

(1) The following planning techniques shall be applied according to the Design Manual to satisfy the minimum control requirements established in Regulation .06 of this chapter:

(a) Preserving and protecting natural resources;

(b) Conserving natural drainage patterns;

(c) Minimizing impervious area;

(d) Reducing runoff volume;

(e) Using ESD practices to maintain 100 percent of the average annual predevelopment groundwater recharge volume for the site;

(f) Using green roofs, permeable pavement, reinforced turf, and other alternative surfaces;

(g) Limiting soil disturbance, mass grading, and compaction;

(h) Clustering development; and

(i) Any practices approved by the Administration.

(2) The following ESD treatment practices shall be designed according to the Design Manual to satisfy the minimum control requirements established in Regulation .06 of this chapter:

(a) Disconnection of rooftop runoff;

(b) Disconnection of nonrooftop runoff;

(c) Sheetflow to conservation areas;

(d) Rainwater harvesting;

(e) Submerged gravel wetlands;

(f) Landscape infiltration;

(g) Infiltration berms;

(h) Dry wells;

(i) Micro-bioretention;

(j) Rain gardens;

(k) Swales;

(l) Enhanced filters; and

(m) Any practices approved by the Administration.

(3) The use of the ESD planning techniques and treatment practices specified in this section may not conflict with existing State law or local ordinances, regulations, or policies. Counties and municipalities shall modify planning and zoning ordinances and public works codes to eliminate any impediments to implementing ESD to the MEP according to the Design Manual.

C. Structural Stormwater Management Measures.

(1) The following structural stormwater management practices shall be designed according to the Design Manual to satisfy the applicable minimum control requirements established in Regulation .06 of this chapter:

(a) Stormwater management ponds;

(b) Stormwater management wetlands;

(c) Stormwater management infiltration;

(d) Stormwater management filtering systems; and

(e) Stormwater management open channel systems.

(2) The performance criteria specified in the Design Manual with regard to general feasibility, conveyance, pretreatment, treatment and geometry, environment and landscaping, and maintenance shall be considered when selecting structural stormwater management practices.

(3) Structural stormwater management practices shall be selected to accommodate the unique hydrologic or geologic regions of the State.

D. Standard Plans.

(1) Compliance with any of the following Standard Plans is considered to satisfy the minimum control requirements established in Regulation .06A(2) of this chapter.

(2) Standard Plans. The following documents are incorporated by reference:

(a) Standard Stormwater Management Plan for Agricultural Structures (SSDS — SP01);

(b) Standard Stormwater Management Plan for Poultry House Development on Marylandís Eastern Shore (SSDS — SP02); and

(c) Standard Stormwater Management Plan for Single Lot Residential Construction (SSDS — SP03).

(3) Compliance with an approved Soil Conservation and Water Quality Plan (SCWQP) is considered to satisfy the minimum control requirements established in Regulation .06A(2) of this chapter if the development:

(a) Is an agricultural structure, or associated access roads and parking areas;

(b) Complies with USDA Natural Resources Conservation Service Maryland Conservation Practice Standard Stormwater Runoff Control Code 570 (March 2013);

(c) Is not located within the Chesapeake and Atlantic Coastal Bays Critical Area; and

(d) Is not subject to the requirements of:

(i) COMAR 26.08.04.09A;

(ii) COMAR 26.08.04.09N; or

(iii) COMAR 26.17.04.05.

(4) An approving agency may require more than the minimum control measures. An approving agency may require that an engineered stormwater management plan be submitted if:

(a) Otherwise required by statute or regulation;

(b) The plan fails to meet ESD to the MEP;

(c) Hydrologic or topographic conditions warrant; or

(d) Flooding, stream channel erosion, or water quality problems exist downstream from a proposed project.

E. County and municipal ordinances shall specify that the ESD planning techniques and treatment practices and structural stormwater management measures used to satisfy the minimum control requirements in Regulation .06 of this chapter are documented and remain unaltered by subsequent property owners. Approval from the appropriate approving agency should be obtained before any stormwater management practice is altered.

F. Alternative ESD planning techniques and treatment practices and structural stormwater management measures may be used for new development runoff control if they meet the performance criteria established in the Design Manual and are approved by the Administration. Practices used for redevelopment projects shall be approved by the appropriate approving agency.

G. For purposes of modifying the minimum control requirements or design criteria, the owner/developer shall submit to the approving agency an analysis of the impacts of stormwater flows downstream in the watershed. The analysis shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications of the proposed development upon a dam, highway, structure, or natural point of restricted streamflow, established with the concurrence of the approving agency, downstream of the first downstream tributary whose drainage area equals or exceeds the contributing area to the project or stormwater management facility.